1. Field of the Invention
The invention relates to an impact modifier additive blend comprised of a core/shell type impact modifier and a terpolymer impact modifier, and to polymeric compositions containing the blend.
2. Description of the Prior Art
Some synthetic resins are widely used as engineering plastics, for example in the building or automotive industries, in particular due to their low cost and to their good physical and/or chemical properties.
Nevertheless, they exhibit low impact strengths at ambient temperature or at low temperature or again also after ageing.
It has been proposed to overcome these defects by incorporating, in these resins, products known as impact additives which are generally polymers exhibiting a degree of elastomeric properties.
Many such additives are known, such as core/shell impact modifiers prepared in emulsion with a first stage or core of a polymer based on butadiene or on a poly(alkyl acrylate), and with one or more shells or second stages based on polymers which are mainly derived from methyl methacrylate, but which may also have polymer chains derived from vinyl aromatic monomers, such as styrene.
Another class of impact modifiers are rubbery linear polymers formed from ethylene, an alkyl acrylate such as ethyl or butyl acrylate, and a third monomer which has a copolymerizable double bond and an available reactive functionality, such as epoxide. A suitable monomer is glycidyl methacrylate (2,3-oxy-1-propyl methacrylate). These rubbery polymers probably are reactive with terminal hydroxyl or carboxyl groups in some resins. They improve the impact strength to some extent, but are known to raise the melt viscosity of the resin substantially, which is deleterious to molding and processing.
Therefore, the problem still exists to find a way to improve the impact strength of polymer without excessive loading of a core/shell modifier, or without increasing the melt viscosity of the blend to an extent where processing is slowed.
We have found that blends of a certain two types of impact modifiers within a certain compositional range offer several unexpected advantages.
First, the impact strength imparted by the blend of impact modifiers is unexpectedly higher than would be predicted by averaging values from blends where only one impact modifier is present. Secondly, the blend imparts acceptable impact strength values while producing a composition of acceptable melt viscosity for injection molding purposes. Thirdly, the blend imparts to the final polymeric composition a desirable combination of weatherability, impact modification and heat stability.